Using tic toc to change a value every 30 seconds?

I am writing a code that creates a bar graph using data created in a matrix. Every 30 seconds, I want to multiply the value of one of the bar graphs by a value. The distortion will increase by 0.02 every time. For example, in the first 30 seconds, the bar graph will show the bar at a normal value (100%), in the second 30 seconds, the bar graph will show the bar at its value times 1.02 (102%), in the third 30 seconds, the bar graph will show the bar at its value times 1.04 (104%). This increases all the way up to 114%, then the distortion decreases from 114% to 112% to 110% etc. back to zero. I have written the code that is capable of doing this and have provided it below (this is all included in a while loop that pulls the data for the bar graphs; "tic" is written before the while loop begins). However, at the beginning of the code and at the end of the code (after it reaches 100%), I want to include a part where the bar graph is at its original value for 2 straight minutes (100% or an alpha value of 0 for 120 seconds). How would I do this if my alpha value is set to increase by 0.02 every time?

if toc > interval

     if alpha <= 1
         distortion = abs(distortion);

     elseif alpha >= 1.14
         distortion = -abs(distortion); 

     end

    alpha = alpha + distortion;
    tic;
end

    array_size = size(M);
    M(array_size(1)+1,:) = [b e Rsteplength Lsteplength];
  if array_size(1) <= row_count
    pause(sampling_time);
    continue;
  else
    row_count = array_size(1);
  end
  
  current_left  = M(row_count,3);
  current_right = M(row_count,4);
  
  if current_left > last_left
    left_bar = current_left*alpha;
  elseif current_left < current_right
    left_bar = 0;
  end
  if current_right > last_right
    right_bar = current_right*alpha;
  elseif current_right < current_left
    right_bar = 0;
  end
  
  
  lstep_length = [left_bar, right_bar];
    bargraph = bar(lstep_length);
  ylim([0,1000])
  
  last_left = current_left;
  last_right = current_right;
    pause(sampling_time);
end

[jgg]

Wouldn't a timer be a better way to do this?

[Geoff Hayes]

jgg has it right. A timer would be a better way to do this. You could then delay the start of the timer by two minutes (when at 100%).